Frontier Airlines was incorporated on February 8, 1994, by a group that included executives of the original incarnation of Frontier Airlines in response to the void left by Continental Airlines 1993 shutdown of its Denver (Stapleton) hub.[14] Scheduled flights began five months later in July 1994 utilizing Boeing 737-200 jetliners on routes between Denver and four destinations in North Dakota: Bismarck, Minot, Fargo and Grand Forks. By January 1995, Frontier had expanded its route network from Denver and was serving Albuquerque, NM, Billings, MT, Bismarck, ND, Bozeman, MT, El Paso, TX, Fargo, ND, Great Falls, MT, Las Vegas, NV, Missoula, MT, Omaha, NE, and Tucson, AZ with Boeing 737 jet service.[15] Like the original airline of the same name, the new Frontier operated a hub at Denver (DEN) and for the first nine years used the slogan "The Spirit of the West" which was displayed above the windows and just behind the cursive letters "Frontier" on the fuselage of their aircraft. In 1999, Frontier signed agreements to begin purchasing and leasing AirbusA318 and A319 jet aircraft and had also added Boeing 737-300 jetliners to its fleet as well. Also by September 1999, the airline was serving destinations from coast to coast in the U.S. having expanded its route network to include Atlanta (ATL), Baltimore (BWI), Bloomington/Normal, IL (BMI), Boston (BOS), Chicago (MDW, Midway Airport), Dallas/Fort Worth (DFW), Phoenix (PHX), Los Angeles (LAX), Minneapolis/St. Paul (MSP), New York City (LGA, LaGuardia Airport), Orlando (MCO), Portland, OR (PDX), Salt Lake City (SLC), San Diego (SAN), San Francisco (SFO) and Seattle (SEA), all served from its Denver hub.[16]

Frontier took delivery of its first Airbus aircraft (an A319) in 2001 and simultaneously launched with it DirecTV in-flight television along with a new company livery. Frontier Airlines was the launch customer[17] of the Airbus A318 in 2003. In mid-April 2005, Frontier officially became an all-Airbus fleet, retiring its last Boeing 737.

As part of its plan to stay competitive in reaction to the entry of Southwest Airlines into Denver, the company underwent a reorganization early in 2006. On April 3, 2006, Frontier created Frontier Airlines Holdings (FRNT), a holding company incorporated in Delaware to take advantage of favorable tax laws in that state. The corporate headquarters did not leave Colorado.[18]

On January 11, 2007, Frontier Airlines signed an 11-year service agreement with Republic Airlines. Under the agreement, Republic was to operate 17, 76-seat Embraer 170 aircraft for the former Frontier JetExpress operations. At the time the contract was canceled in April 2008, Republic Airlines operated 11 aircraft for Frontier Airlines, with the remaining six aircraft expected to join the fleet by December 2008. With the integration of Republic aircraft, the 'JetExpress' denotation was removed. Subsequent to the cessation of Horizon's services for Frontier in December 2007, all flights operated by Republic were sold and marketed as "Frontier Airlines, operated by Republic Airlines." The first market created specifically for the Embraer 170 was Louisville, Kentucky, which began on April 1, 2007. Service to Louisville was suspended in August 2008 but restarted in April 2010.

Flights operated by Republic Airlines offered in-flight snack and beverage services similar to Frontier's mainline flights. Unlike Frontier's aircraft and due to the nature of contracting with regional carriers, these Embraer 170 aircraft were not fitted with LiveTV.

On April 10, 2008, Frontier filed for Chapter 11 bankruptcy in reaction to the intent of its credit card processor, First Data, to withhold significant proceeds from ticket sales.[20] First Data decided that it would withhold 100% of the carrier's proceeds from ticket sales beginning May 1.[21] According to Frontier's press release, "This change in practice would have represented a material change to our cash forecasts and business plan. Unchecked, it would have put severe restraints on Frontier's liquidity..." Its operation continued uninterrupted, though, as Chapter 11 bankruptcy protected the corporation's assets and allowed restructuring to ensure long-term viability.

After months of losses, Frontier Airlines reported that they made their first profit during the month of November 2008. Frontier Airlines reported $2.9 million in net income during the month of November.[22]

On June 22, 2009, Frontier Airlines announced that pending bankruptcy court approval, Republic Airways Holdings, the Indianapolis-based parent company of Republic Airlines, would acquire all assets of Frontier Airlines for the amount of $108 million. Thus, Frontier Airlines would become a wholly owned subsidiary of Republic.[23] However, 5 weeks later on July 30, Dallas-based Southwest Airlines announced that it would be making a competing bid of $113.6 million for Frontier with intentions to also operate Frontier as a wholly owned subsidiary, but that it would gradually fold Frontier resources into current Southwest operating assets.[24]

During a bankruptcy auction on August 13, 2009, Republic Airways Holdings acquired Frontier Airlines and its regional airline, Lynx Aviation, as wholly owned subsidiaries.[25] Republic completed the transaction on October 1, 2009, and Frontier officially exited bankruptcy as a new airline.[26]

In late 2009 Republic began to consolidate administrative positions and moved 140 jobs from the Frontier Airlines Denver headquarters to Indianapolis, Indiana.[27] Shortly after that, in January 2010, Republic Airways announced that it would move all of its executives to Indianapolis.[28] In February the Denver Business Journal stated that the headquarters would be moved "soon."[29] Despite this, according to the Denver Business Journal, Frontier Airlines will still maintain a local headquarters in Denver to house Training, Marketing, Customer Reservations, and Scheduling & Planning teams after extending its lease on the building through 2020.

As Republic Airways Holdings was in the process of bidding to acquire Frontier in 2009, it was also in the process of acquiring Milwaukee-based Midwest Airlines. Through the fall and winter of 2009, Republic operated its two new acquisitions as separate brands. However, to improve efficiency by better matching aircraft capacity to route demand, Republic began to intermix the fleets of the two airlines, swapping a portion of its higher-capacity planes from Frontier with its smaller-capacity planes from Midwest and vice versa. However, the move caused some confusion amongst the public, as the two brands did not offer the same amenities and did not match the amenities mentioned on the airfare. As a result, in the Spring of 2010, Frontier and Midwest Airlines announced that their brands would merge, with Frontier being the surviving brand.[31] This was a merger of brands only—no Midwest Airlines aircraft was ever operated by Frontier, as by this time, all Midwest Airlines flights were operated on its behalf by other Republic Airways Holdings subsidiaries.

On April 13, 2011, Frontier formed a new subsidiary, Frontier Express, that was planned to operate the airline's smaller aircraft with different services than those available on full-size aircraft.[32]

After merging with Midwest Airlines, Frontier cut 11 out of its 18 flights leaving a total of just 7 from Milwaukee's MKE to Denver, Orlando, Rhinelander and Washington-National.[33] At its peak, Frontier operated around 50-80 flights from Milwaukee daily.

On September 9, 2011, Frontier notified the public of a 40% reduction of arriving and departing flights from MKE. Along with this reduction of flights, the company laid off approximately 140 employees from the MKE station. This includes but is not limited to: maintenance, grooming services, flight-line and gate.[34]

In February 2012, Frontier Airlines cut five nonstop routes from Milwaukee. This move "reduced Frontier's daily departing flights out of Mitchell International from 32 to 18," or 56%. Frontier announced further layoffs in conjunction with this route change: up to 446 Milwaukee-area employees were affected by the job cuts that occurred between April 15 and April 30, 2012.[35]

In an effort to focus on regional contract flights for major carriers, Republic Airways Holdings announced in January 2012 its intention to sell or spin off Frontier.[13][36] On January 26, 2012, Republic Airways Holdings appointed former US Airways and Gate Gourmet CEO David Siegel as President and CEO of Frontier Airlines. Republic also added new senior officers for Frontier’s finance and commercial team, among other changes in the executive leadership team. Siegel and other Frontier executives moved to Denver where Frontier is headquartered in order to facilitate management of all aspects of Frontier during its separation process from Republic and continue its transformation into an ultra-low-cost carrier.[10]

Frontier marketed both the Trenton-Mercer and Wilmington-Philadelphia airports as low-cost, low-hassle alternatives to the existing nearby commercial airports. Frontier was the only commercial carrier at these two airports.

In January 2015, Frontier Airlines cut several flights from Wilmington and Trenton. It also resumed service to Philadelphia, casting doubt on the airline's existing bases.[40][41] In late June 2015, Frontier announced it had ceased service in Wilmington, stating it was not profitable.[42]

In October 2013, Republic Airways Holdings entered into an agreement with private equity firm Indigo Partners to sell Frontier Airlines for approximately $145 million. According to Indigo, the transaction would further Frontier’s evolution into an ultra-low-cost carrier.[13] In December 2013, Indigo Partners LLC, through an affiliate, completed the purchase of Frontier Airlines from Republic Airways Holdings. The airline's headquarters will remain in Denver.[43] Republic Airways Holdings subsidiary Republic Airlines no longer flies Embraer 190 aircraft on behalf of Frontier, as of January 1, 2014.

In 2014, Frontier announced it would be transitioning into an ultra-low cost carrier.[44] Frontier will also cut several flights and jobs at their Denver hub and transition them to different markets. On January 16, 2015 Frontier announced that it will close both its Denver and Milwaukee call centers, laying off 1,300 employees and outsourcing the jobs to call center company, Sitel.[45]

In May 2015, Indigo and Frontier announced the departure of David Siegel as CEO. He had already previously turned over the role of president to Barry Biffle, formerly of Spirit Airlines. Siegel was not immediately replaced. Instead, his duties were split between Biffle and Indigo chairman Bill Franke. Biffle cited operational issues in connection with Siegel's departure.[46]

All Frontier Airlines aircraft feature slimline seating. Main cabin seats are pre-reclined. "Stretch" row seating features a reclining seat, lumbar support and diamond stitching which are sold for an additional charge. There are no televisions in any of the seats. The middle seats are the widest of any airline in the United States. Frontier did this to lower their cost per seat by 30%.

Chautauqua Airlines operated up to 12 Embraer 135 and 145 jets out of Milwaukee. Frontier began branding these flights as Frontier Express in the spring of 2011. With the pull-down of the Milwaukee hub, the only route that continued to operate with a Frontier Express ERJ-145 jet was Milwaukee to Rhinelander. However, Frontier service to Rhinelander ended on January 3, 2013, and Chautauqua transferred the remaining aircraft to other partners.

In February 2002, the airline launched its first regional product, Frontier JetExpress, initially operated by Mesa Airlines using CRJ-200 regional jets. Similar to "express" operations of other carriers, Frontier JetExpress was targeted for markets to and from Denver that do not generate traffic sufficient to support Frontier's smallest mainline jet, the Airbus A318, but could still offer lucrative business with a smaller jet.

The initial JetExpress partnership with Mesa ended in January 2004, when Horizon Air was selected to operate the routes. Horizon utilized slightly larger CRJ-700 aircraft on these routes. In August 2006, Frontier and Horizon ended their partnership.[50] While Frontier was generally pleased with Horizon's operation, the carrier decided that it needed to revisit the agreement and find a provider with additional regional jets to grow the operation. The last of the CRJ-700's was returned to the Horizon Air fleet on November 30, 2007.

On September 6, 2006, Frontier created a new division of the holding company, known as Lynx Aviation, to operate Bombardier Q400 aircraft beginning in May 2007.[51] On December 5, 2007, Lynx Aviation received its operating certificate from the FAA. Lynx began passenger operations on the morning of December 6, 2007.

In 2012, the Lynx Aviation operation was folded into Republic Airways Holdings subsidiary Republic Airlines. The remaining Q400 aircraft were withdrawn from Frontier service and placed in service for United Airlines.

In 1997, Maverick Airways was operating code share service for Frontier with de Havilland Canada DHC-7 Dash 7STOL capable turboprops between Denver (DEN) and two destinations in Colorado: Grand Junction (GJT) and Steamboat Springs (SBS).[52] However, the service was short lived as Maverick encountered financial challenges and then ceased all flights.

During the 2011 Paris Air Show, Republic Airways Holdings ordered 60 A320neo aircraft and 20 A319neo aircraft for Frontier.[54] In 2014 the airline ordered 19 Airbus A321neos.[55] In October 2016 Frontier Airlines took delivery of its first Airbus A320neo aircraft (of 80) and became the second US operator (after Spirit Airlines) of the type.[56]

From 1994 to 2003, the airline's livery consisted of green script "Frontier" titles on the forward fuselage, a small "Spirit of the West" slogan, and wildlife photography on the tail of each aircraft.[58] Most Boeing 737 aircraft featured different imagery on both sides.[59]

Beginning in 2001, a new livery was introduced on the airline's new Airbus A319s, with large silver "FRONTIER" titles on the sides of the aircraft, and the airline's "Spirit of the West" slogan, later changed to "A whole different animal." The animal tails were retained, although only one image per aircraft was now used. Though the airline's Boeing 737s remained in the fleet until 2005, none were repainted into this livery.

In April 2013, Frontier introduced a modified version of that livery,[60] keeping the iconic animals on aircraft tails, but dropping its former slogan and replacing "FRONTIER" with "FLYFRONTIER.COM", the company's website, in support of new marketing that focused heavily on the airline's web presence. This livery was only painted on a few newly delivered aircraft. Aircraft in the older livery received "FLYFRONTIER.COM" titles on engine nacelles.

On September 9, 2014, Frontier introduced an updated livery,[61] as part of a rebranding that saw the spokesanimals' roles increase. The new livery reintroduced a green "FRONTIER" typeface to the fuselage, featuring the stylized "F" designed by Saul Bass for the original Frontier in 1978. Each aircraft features the name of the animal featured on its tail near the nose of the aircraft for easier identification. Currently about fifteen aircraft in the Frontier fleet feature the new livery.

Frontier Airbus A321 in the current livery at Cleveland Hopkins International Airport

Animal concepts used in the livery extend into Frontier’s marketing as well. Each animal has a specific name.[62] Animal aircraft used in their radio and television commercials include Jack the rabbit, Grizwald the bear, Foxy the fox (for whom Jack has a crush), Flip the dolphin (who always gets stuck going to Chicago rather than the warmer climates the others are going to), Larry the lynx, Hector the sea otter, and Sal the cougar. New additions are Penguins Jim, Joe, Jay, and Gary, a barbershop-style quartet, singing the praises of EarlyReturns to an audience of Frontier’s well-known characters from the "a whole different animal" campaign, Hector the otter, advertising Frontier's expanding service to Mexico, and Polly the Parrot, who won the new animal audition in 2012.